The term “electric vehicle” as used herein, includes vehicles having an electric motor for vehicle propulsion, such as battery electric vehicles (BEV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV). A BEV includes an electric motor, wherein the energy source for the motor is a battery that is re-chargeable from an external electric grid. In a BEV, the battery is the source of energy for vehicle propulsion. A HEV includes an internal combustion engine and an electric motor, wherein the energy source for the engine is fuel and the energy source for the motor is a battery. In a HEV, the engine is the main source of energy for vehicle propulsion with the battery providing supplemental energy for vehicle propulsion (the battery buffers fuel energy and recovers kinematic energy in electric form). A PHEV is like a HEV, but the PHEV has a larger capacity battery that is rechargeable from the external electric grid. In a PHEV, the battery is the main source of energy for vehicle propulsion until the battery depletes to a low energy level, at which time the PHEV operates like a HEV for vehicle propulsion.
The electric motor is connected to at least two wheels by a transmission or gearbox. The motor provides output torque to the wheels through the gearbox for propelling the vehicle. The motor may also receive input torque from the wheels through the gearbox for generating electricity and braking the vehicle (regenerative braking). Electric vehicles often include a braking system that utilizes both friction braking and regenerative braking Regenerative braking is used to recharge vehicle batteries, and recovers much of the energy that would otherwise be lost as heat during friction braking Therefore regenerative braking improves the overall efficiency or fuel economy of the electric vehicle as compared to vehicles only configured for friction braking.
During regenerative braking, interactions between an antilock braking system (ABS) of the vehicle, the powertrain and the road surface can result in deflections in the powertrain (i.e., powertrain oscillations). The powertrain oscillations can cause unpleasant noise and vibration, and can damage powertrain components over time. The powertrain may include a disengagement mechanism, such as a clutch, which may be utilized to reduce such powertrain oscillation. However, a powertrain that does not include a disengagement mechanism is susceptible to such powertrain oscillations during regenerative braking.